1. Field of the Invention
The field of art to which this invention relates is display devices. It is more particularly directed to transmissive displays.
2. Description of the Related Art
It is a constant endeavor to find ways of improving display device design and manufacturing techniques. This is particularly important as developing display technologies require smaller and smaller pixel sizes. Among other things, this requires that the aperture ratios of transmissive liquid crystal devices be maximized to increase light throughput and/or to save battery power. These are both important criteria in judging the performance of a transmissive display. Currently the achieved pixel aperture ratios of transmissive liquid crystal devices are around 50-60% for amorphous direct view displays, and 30-50% for polysilicon or single crystal silicon panels. This also has utilization for projection displays and head-mounted displays. As the number of pixels in the liquid crystal panel is increased, the aperture ratio is decreased if special design techniques are not implemented. The aperture ratio is the ratio of area occupied by the clear portion of the pixel to that occupied by the light obscuring portion.
The light obscuring portion includes a thin film transistor, a storage capacitor and the display row and column lines. Consequently, the aperture ratio of display devices must be carefully engineered in order to stay competitive in the transmissive display area.
It is known that the apparent aperture ratios of transmissive liquid crystal display devices can be increased by focusing light into the transparent area using a microlens array on a per pixel basis. One way to increase the pixel light throughput, is to focus the light into the clear area of each pixel using a microlens array. A prior art microlens array is fabricated on the color filter side of the LCD panel. More specifically, the microlens array is placed inside the cell facing the liquid crystal, as shown in FIG. 1. This solution requires major modification of the processing steps and effects the reliability, cost and manufacturing yield of the device. FIG. 1 shows a borosilicate glass 110, having sealing material 150 disposed upon it such as to form an outline of the display. Liquid crystal 160 material is included within the outline. A top substrate 180 includes a layer of plastic film 130, disposed upon the liquid crystal 160 material. A microlens array is affixed upon a glass carrier 120 disposed upon the plastic film.
The liquid crystal display devices of the prior art employ a structure consisting of a top glass substrate containing the color filters 200, a bottom glass substrate containing the thin film transistor 210, and back light (not shown). The space between the two glass substrates is taken up by the liquid crystal 160. A rubbing layer 220 is formed adjacent to the liquid crystal material to orient the crystals.